Glass sheets are heated to a softened condition in order to perform forming and other processing. One type of forming such as disclosed by U.S. Pat. No. 4,282,026 McMaster et al involves transferring of the heated glass sheet from a heating conveyor to a downwardly facing planar surface of a vacuum platen from which the heated glass sheet is subsequently transferred to a mold for forming to a desired shape. Engagement of the glass sheet with the downwardly facing surface of the vacuum platen can adversely affect the glass surface by markings or other small deformations that can destroy optical quality.
U.S. Pat. No. 3,223,443 Misson discloses what appears to be experimental apparatus for handling of small sample size heated glass sheets by a pressure control support bed that faces downwardly and supports the glass sheet without any direct engagement. This support bed includes a plate from which tubes extend downwardly and have lower ends with inverted cups that are spaced from each other. Pressurized gas is supplied from a plenum above the plate through the tubes to the interior of the cups and a vacuum is drawn between the cups so as to thereby provide both pressurized gas and a vacuum that provides the support of the glass sheet without any direct engagement. However with this construction, thermal warpage of the plate upon heating and cooling during actual use in a factory condition can result in movement between the inverted cups which adversely affects the uniformity of pressurized gas and vacuum and hence the capability of the support bed to support the glass sheet at a constant elevation without flutter. In a modified embodiment, the pressurized gas is supplied through a porous bottom plate and the vacuum is drawn through tubes that project through the bottom plate and have upper ends supported by another plate spaced below the bottom plate. Gas under pressure is thus supplied through small pores in the bottom plate of a size that is disclosed as being preferably in the range of about 0.0002 to 0.025 of an inch, i.e., about 0.05 to 0.065 cm. With such a construction, the pressurized gas is not supplied with sufficient velocity so as to be capable of producing jets spaced from the tubes through which the vacuum is drawn and the capability of this modified support bed to support larger glass sheets is thus questionable.
U.S. Pat. Nos. 4,578,013 and 4,615,724 of Fackelman disclose glass sheet processing including topside transfer apparatus whose preferred embodiment is a refractory platen that supplies pressurized gas and a vacuum to a downwardly facing surface to support a heated glass sheet during transfer from a heating conveyor to a bending mold. The refractory platen is preferably made of fused silica so as to have good resistance to thermal warpage during heating and cooling and thereby overcomes problems associated with the aforementioned Misson patent whose disclosed support bed did not have sufficiently operable structure so as to be capable of functioning in a commercial factory as opposed to merely being used for experimental purposes.